1. FIELD OF THE INVENTION
The invention relates to a bolt for being driven into bone tissue and an intramedullary nail locked in a bone with such a bolt.
2. DESCRIPTION OF THE PRIOR ART
Stabilizing aids, plates for osteosynthesis, prostheses for joints, intramedullary nails, etc. are usually fixed to the bone by means of screws or profiled nails. Typical screws and nails of this kind are described in CH 670 754 and CH 669 724.
These conventional screws and nails are provided with a threading, barb-like ridges, or similar irregularities extending over at least part of their shank for preventing the bolts from slipping out of the bone. They have therefore an irregular surface, which can lead to manyfold problems. If such screws or nails are e.g. subjected to static or dynamic stress, they cause an inhomogeneous distribution of pressure in the bone tissue. High peak pressures are e.g. found at the edge of a threading or a ridge. Such high pressure can cause a resorption of bone tissue and thereby weaken the bone and loosen the screw or nail, respectively. This can lead to an undesired distribution of forces in the bone and a fracturing of bone, screw, or nail.
If a screw is e.g. driven through a tubular bone and screwed with its tip into the hard bone tissue lying opposite its head, the described effect can lead to a loosening of the screwed tip and a redistribution of forces towards the head of the screw and, resulting in breaking of the screw or damaging of the bone tissue at the head of the screw.
Furthermore, conventional screws are not rotationally stable, i.e. they can be rotated and thereby loosened, which again leads to additional forces and an inhomogeneous distribution of pressure and can therefore damage the screw or the bone.
Furthermore, most conventional solutions require that holes are drilled into the bone or even that a threading must be cut in the bone tissue prior to inserting the screw or nail. This leads to an additional working step. It also causes a loss of bone material and thereby a further weakening of the bone.